1. Field of the Invention
The present invention relates to electric arc lamps, and more particularly concerns dynamic stabilization of arc position and intensity.
2. Description of Related Art
The high intensity white light source employed by many optical systems, such as video and film projectors, is commonly produced by an electric arc lamp. The arc of such a lamp is subject to wander, that is, a random shift of the arc relative to one of the electrodes in a plane transverse to the direction in which the arc extends between the electrodes. Such arc wander causes an undesired flicker (amplitude variation) of the projected image which is sometimes masked by defocusing of the illumination source, thereby decreasing optical efficiency.
Prior arc lamps employ a pointed electrode for the cathode which burns and becomes blunt during the life of the lamp. At least partly for this reason, arc lamp output decreases considerably in the first one hundred hours of use. The cathode burnback not only causes variation of arc light intensity and arc position, but decreases lamp life and limits lamp current modulation range.
Arc lamp wander is essentially of a random nature, and cannot be specifically predicted. It may be due to a number of factors, including gas turbulence, current changes, preferential electron emitter sites on the cathode, and also external magnetic fields In the past, permanent magnets have been employed to cancel fixed external magnetic fields, but applicant is not aware of any attempt made to correct for arc wander due to other factors, such as gas turbulence, current changes and preferential electron emitter sites. No dynamic stabilization of an arc has been previously employed. Prior art has merely attempted to mask the arc wander by defocusing, or more generally, has simply tolerated the undesirable flicker.
Accordingly, it is an object of the present invention to stabilize an electric arc so as to decrease wander and intensity variation.